This invention relates to systems and techniques that are used to enhance the performance of data communication systems employing differential signaling techniques; and more particularly, in one aspect, to enhance the performance of data communication systems, using differential signaling, implemented in wired type environments such as microstrip, stripline, printed circuit board (for example, a backplane), and integrated circuit (IC) package.
Communications systems are continuing to increase the rate at which data is transmitted between devices. The increase in data rate presents a challenge to maintain, enhance or optimize the ability to recover the transmitted signal and thereby the information contained therein. In general, increasing the rate of transfer of data tends to adversely impact the fidelity of the communications.
In the context of communications systems employing differential signaling, the layout of the signal path in, for example, a backplane or printed circuit board environment, may impact the ability of the receiver to recover the transmitted information. Conventional systems tend to layout the signal paths of differential signal pairs in a manner that minimizes or eliminates skew (relative time delay) between the differential signal pair. As such, conventional systems tend to layout signal paths so that differential signal pairs are transmitted on paths having the shortest and equal lengths. In this way, the contribution to skew (of a differential signal pair) as a result of the signal path layout in a backplane or printed circuit board environment is minimized or substantially eliminated.
For example, with reference to FIGS. 1 and 2A,2B, 2C, a conventional data communications system typically includes a layout or routing of differential signal pair 2 such that signal paths 4 and 4′ are equal (and the shortest) lengths. Similarly, differential signal pair 6 may be transmitted on signal paths 8 and 8′, which are also equal in length. As such, the layout of the signal paths is unlikely to introduce additional skew between the respective signal pairs 2 and 6. (See, for example, U.S. Pat. Nos. 6,249,544 and 6,252,904). This is significant because the receiver employs the difference between the signals of the differential signal pairs, sampled at a particular time, in order to recover the transmitted information.
While conventional systems avoid certain debilitating affects on the fidelity of the differential signal as a result of skew between the differential signal pair, such systems tend to experience significant coupling or crosstalk from adjacent signals (for example, inductive and/or capacitive coupling) which adversely impacts the ability of the receiver to recover the transmitted information. For example, with continued reference to FIG. 1, the signal transmitted on signal path 4 is likely to experience cross coupling, at the vias or connector pins, between the signal on signal path 8. Similarly, the signal transmitted on signal path 4′ is likely to experience cross coupling, at the vias or pins, between the signal on signal path 8′.
Conventional systems often address such crosstalk using circuitry, additional insulation materials to “shield” the signals, and/or intricate layout techniques. (See, for example, U.S. Pat. Nos. 6,266,730, 6,420,778, 6,449,308, and 6,570,944 and U.S. Patent Application Publication 2003/014375). Such conventional crosstalk reduction techniques may be quite complicated to implement as well as expensive. In this regard, systems that employ crosstalk reduction circuitry tend to consume power and space/area, for example, on the die or printed circuit board. Further, conventional systems that employ additional materials to “shield” the signals and/or complicated layout techniques are often expensive, and/or the layout techniques may be quite complicated and susceptible to manufacturing tolerances, which are often quite strict.
There is a need for a system and technique that overcomes the shortcomings of one, some or all of conventional systems. In this regard, there is a need for an improved crosstalk reduction or management technique that is less complicated and expensive than conventional circuitry and techniques and that overcomes one, some or all of the shortcomings of conventional systems.